1. Field of the Invention
The present invention relates to a camera comprising a drive ring rotatable around an image-taking optical axis, which drives a lens member and a driven unit by rotation of the drive ring.
2. Description of the Related Art
In conventional methods, in order to allow the lens barrel of a camera to advance and retract in the direction of the image-taking optical axis, a driving force from an actuator such as a motor is transmitted by a gear etc., to a rotating member arranged outside the lens barrel, a lens holding member that holds an image-taking lens is moved in the direction of the image-taking optical axis by rotation of the rotating member around the image-taking optical axis. Herein, the rotating member and the lens holding member are engaged by cams and helicoids, etc., and the lens holding member can be moved in the direction of the image-taking optical axis in response to the rotation of the rotating member in a state where the lens holding member is prevented from rotating.
On the other hand, a camera is available that is provided with an inner circumferential gear inside a rotating member so as to reduce the size of a lens barrel. In the lens barrel disclosed in Japanese Patent Application Laid-Open No. H7(1995)-174954, a helical inner circumferential gear is formed on a rotating member.
In the structure of the above-mentioned lens barrel, the rotating maker needs to receive a driving force from an actuator so that the lens holding member is moved in the direction of the image-taking optical axis by the rotation of the rotating member around the image-taking optical axis. For this purpose, gear portion that engage with gears interconnected to an actuator must be formed on the rotating member.
In addition, in case that the lens holding member (image-taking lens) is allowed to move together with a lens constituting a finder optical system arranged outside the lens barrel by the rotation of the rotating member, it is necessary to transmit the rotational force of the rotating member to a finder unit having the finder optical system through a gear train. Therefore, it is necessary to form gear portion which engage with gears interconnected to the finder unit on the rotating member.
Herein, in case that an inner circumferential gear portion for receiving a driving force from the actuator is formed on the inner surface of the cylindrically-shaped rotating, it is necessary to make the thickness of the rotating member (thickness in the diameter direction of the rotating member) greater than in a case where an inner circumferential gear portion is not formed, in order to secure the strength of the rotating member. Further, in case that an outer circumferential gear portion for transmitting a driving force to the finder unit is formed on the outer surface of the rotating member, the thickness of the rotating member must be great.
In addition, in case that the inner circumferential gear portion and the outer circumferential gear portion are formed within the plane orthogonal to the image-taking optical axis, the thickness of the rotating member must be greater still.
As explained above, a greater thickness of the rotating member results in an increased size of the rotating member in the diameter direction, thereby resulting in an increased size of a lens barrel and a camera provided with the lens barrel. Further, in case that the outer circumferential gear portion of the rotating member is interconnected to the finder unit, the finder unit is kept away from the lens barrel by a distance of the increased thickness of the rotating member, thus making the distance between an image-taking optical axis and a finder optical axis longer, which then results in a greater parallax.